This invention relates generally to microscopes and particularly to a projection microscope having high magnification and resolution.
The device known as a microscope has been available since about 1650. Essentially, such devices provide a means of making objects appear much larger than they are and are particularly useful for the study of biological specimens. They consist of an illumination source that lights the specimen, a stage that holds the specimen in place and, above all an optical system that provides the requisite degree of magnification, that is, the size of the image of the specimen compared with the actual size of the specimen. The image is viewed by the human eye or a technological substitute for the eye, such as a video camera.
Conventional compound microscopes comprise essentially of two optical elements, namely, an objective lens and an ocular lens. The objective lens forms a real, aerial inverted image at some point along the optical axis of the system. Conventionally, this inverted image is located at a point inside the front focal length of the ocular lens. The ocular lens on the other hand, accepts ray bundles from the aerial image and forms a magnified virtual image located at, or close to, infinity. Accordingly, the eye receives collimated light which is necessary for ease of observation. Usually, the aerial image distance and the focal length of the ocular lens are accommodated within the length of the microscope barrel, usually about 6 ins.–8 ins. long.
There have been many attempts to improve on the basic microscope discussed above but most improvements, particularly to the optical system tend to be very expensive, with little gained for the high cost. Accordingly, individual microscopes with high quality magnification and resolution are out of the economic reach of schools, and similar teaching establishments which prefer to have one microscope for each student.
Several prior art references disclose the use of a folded light path, which increases the length of the light path. References of particular interest are U.S. Pat. No. 4,818,084 (Wentz III); U.S. Pat. No. 5,969,852 (Kung), and U.S. Pat. No. 4,537,483 (Turner). All three references employ the same principle wherein the ocular lens of a conventional microscope is replaced by an optical system which projects a real image onto a rear projection screen. In the case of Turner and Wentz III the projection screen is viewed using a large diameter low power lens which provides additional image magnification. Neither one, however, provides the high magnification at low cost. Also U.S. Pat. No. 5,671,085 (Gustafsson, et al.) discloses the use of opposing objective lens but in a specific arrangement directed to stereoscopic imagery. These four patents are incorporated herein by reference.
It is the aim of this invention to provide a projection microscope that overcomes these problems in a manner which results in an efficient yet cost effective instrument.